While most fungi have the ability to reproduce sexually, multiple independent lineages have lost meiosis and developed parasexual cycles in its place. Emergence of parasexual cycles is particularly prominent in medically relevant fungi from the CUG paraphyletic group of Candida species. Since the discovery of parasex in C. albicans roughly two decades ago, it has served as the model for Candida species. Importantly, parasex in C. albicans retains hallmarks of meiosis including genetic recombination and chromosome segregation, making it a potential driver of genetic diversity. Furthermore, key meiotic genes play similar roles in C. albicans parasex and highlights parallels between these processes. Yet, the evolutionary role of parasex in Candida adaptation and the extent of resulting genotypic and phenotypic diversity remain as key knowledge gaps in this facultative reproductive program. Here, we present our current understanding of parasex, the mechanisms governing its regulation, and its relevance to Candida biology. more »« less
ABSTRACT Fungi were some of the earliest organismal systems used to explore mutational processes and its phenotypic consequences on members of a species. Yeasts that cause significant human disease were quickly incorporated into these investigations to define the genetic and phenotypic drivers of virulence. AmongCandidaspecies,Candida albicanshas emerged as a model for studying genomic processes of evolution because of its clinical relevance, relatively small genome, and ability to tolerate complex chromosomal changes. Here, we describe major recent findings that used evolution of strains from defined genetic backgrounds to delineate mutational and adaptative processes and include how nascent exploration into naturally occurring variation is contributing to these conceptual frameworks. Ultimately, efforts to discern adaptive mechanisms used byC. albicanswill continue to divulge new biology and can better inform treatment regimens for the increasing prevalence of fungal disease.
ABSTRACT Candida albicans is an opportunistic fungal pathogen of humans that is typically diploid yet has a highly labile genome tolerant of large-scale perturbations including chromosomal aneuploidy and loss-of-heterozygosity events. The ability to rapidly generate genetic variation is crucial for C. albicans to adapt to changing or stressful environments, like those encountered in the host. Genetic variation occurs via stress-induced mutagenesis or can be generated through its parasexual cycle, in which tetraploids arise via diploid mating or stress-induced mitotic defects and undergo nonmeiotic ploidy reduction. However, it remains largely unknown how genetic background contributes to C. albicans genome instability in vitro or in the host environment. Here, we tested how genetic background, ploidy, and the host environment impacts C. albicans genome stability. We found that host association induced both loss-of-heterozygosity events and genome size changes, regardless of genetic background or ploidy. However, the magnitude and types of genome changes varied across C. albicans strain background and ploidy state. We then assessed if host-induced genomic changes resulted in fitness consequences on growth rate and nonlethal virulence phenotypes and found that many host-derived isolates significantly changed relative to their parental strain. Interestingly, diploid host-associated C. albicans predominantly decreased host reproductive fitness, whereas tetraploid host-associated C. albicans increased host reproductive fitness. Together, these results are important for understanding how host-induced genomic changes in C. albicans alter its relationship with the host. IMPORTANCE Candida albicans is an opportunistic fungal pathogen of humans. The ability to generate genetic variation is essential for adaptation and is a strategy that C. albicans and other fungal pathogens use to change their genome size. Stressful environments, including the host, induce C. albicans genome instability. Here, we investigated how C. albicans genetic background and ploidy state impact genome instability, both in vitro and in a host environment. We show that the host environment induces genome instability, but the magnitude depends on C. albicans genetic background. Furthermore, we show that tetraploid C. albicans is highly unstable in host environments and rapidly reduces in genome size. These reductions in genome size often resulted in reduced virulence. In contrast, diploid C. albicans displayed modest host-induced genome size changes, yet these frequently resulted in increased virulence. Such studies are essential for understanding how opportunistic pathogens respond and potentially adapt to the host environment.
Gregor, Justin B.; Gutierrez-Schultz, Victor A.; Hoda, Smriti; Baker, Kortany M.; Saha, Debasmita; Burghaze, Madeline G.; Vazquez, Cynthia; Burgei, Kendra E.; Briggs, Scott D.
(, mSphere)
Mitchell, Aaron P.
(Ed.)
ABSTRACT The World Health Organization recently published the first list of priority fungal pathogens highlighting multipleCandidaspecies, includingCandida glabrata,Candida albicans, andCandida auris. However, prior studies in these pathogens have been mainly limited to the use of two drug resistance cassettes,NatMXandHphMX, limiting genetic manipulation capabilities in prototrophic laboratory strains and clinical isolates. In this study, we expanded the toolkit forC. glabrata,C. auris, andC. albicansto includeKanMXandBleMXwhen coupled with anin vitroassembled CRISPR-Cas9 ribonucleoprotein (RNP)-based system. Repurposing these drug resistance cassettes forCandida, we were able to make single gene deletions, sequential and simultaneous double gene deletions, epitope tags, and rescue constructs. We applied these drug resistance cassettes to interrogate the ergosterol pathway, a critical pathway for both the azole and polyene antifungal drug classes. Using our approach, we determined for the first time that the deletion ofERG3inC. glabrata,C. auris,andC. albicansprototrophic strains results in azole drug resistance, which further supports the conservation of the Erg3-dependent toxic sterol model. Furthermore, we show that anERG5deletion inC. glabratais azole susceptible at subinhibitory concentrations, suggesting that Erg5 could act as an azole buffer for Erg11. Finally, we identified a synthetic growth defect when bothERG3andERG5are deleted inC. glabrata,which suggests the possibility of another toxic sterol impacting growth. Overall, we have expanded the genetic tools available to interrogate complex pathways in prototrophic strains and clinical isolates. IMPORTANCEThe increasing problem of drug resistance and emerging pathogens is an urgent global health problem that necessitates the development and expansion of tools for studying fungal drug resistance and pathogenesis. Prior studies inCandida glabrata,Candida auris, andCandida albicanshave been mainly limited to the use ofNatMX/SAT1andHphMX/CaHygfor genetic manipulation in prototrophic strains and clinical isolates. In this study, we demonstrated thatNatMX/SAT1, HphMX, KanMX,and/orBleMXdrug resistance cassettes when coupled with a CRISPR-ribonucleoprotein (RNP)-based system can be efficiently utilized for deleting or modifying genes in the ergosterol pathway ofC. glabrata,C. auris, andC. albicans. Moreover, the utility of these tools has provided new insights intoERGgenes and their relationship to azole resistance inCandida. Overall, we have expanded the toolkit forCandidapathogens to increase the versatility of genetically modifying complex pathways involved in drug resistance and pathogenesis.
Smith, Amanda; Morran, Levi; Hickman, Meleah A.
(, Infection and Immunity)
The ability to generate genetic variation facilitates rapid adaptation in stressful environments. The opportunistic fungal pathogen Candida albicans frequently undergoes large-scale genomic changes, including aneuploidy and loss-of heterozygosity (LOH), following exposure to host environments. However, the specific host factors inducing C. albicans genome instability remain largely unknown. Here, we leveraged the genetic tractability of nematode hosts to investigate whether innate immune components, including antimicrobial peptides (AMPs) and reactive oxygen species (ROS), induced host-associated C. albicans genome instability. C. albicans associated with immunocompetent hosts carried multiple large-scale genomic changes including LOH, whole chromosome, and segmental aneuploidies. In contrast, C. albicans associated with immunocompromised hosts deficient in AMPs or ROS production had reduced LOH frequencies and fewer, if any, additional genomic changes. To evaluate if extensive host-induced genomic changes had long-term consequences for C. albicans adaptation, we experimentally evolved C. albicans in either immunocompetent or immunocompromised hosts and selected for increased virulence. C. albicans evolved in immunocompetent hosts rapidly increased virulence, but not in immunocompromised hosts. Taken together, this work suggests that host-produced ROS and AMPs induces genotypic plasticity in C. albicans which facilitates rapid evolution.
King, William R.; Acosta-Zaldívar, Maikel; Qi, Wanjun; Cherico, Nicholas; Cooke, Lauren; Köhler, Julia R.; Patton-Vogt, Jana
(, mSphere)
Lorenz, Michael
(Ed.)
ABSTRACT The fungal pathogenCandida albicansmust acquire phosphate to colonize, infect, and proliferate in the human host.C. albicanshas four inorganic phosphate (Pi) transporters, Pho84 being the major high-affinity transporter; its cells can also use glycerophosphocholine (GPC) as their sole phosphate source. GPC is a lipid metabolite derived from deacylation of the lipid phosphatidylcholine. GPC is found in multiple human tissues, including the renal medulla, where it acts as an osmolyte.C. albicansimports GPC into the cell via the Git3 and Git4 transporters. Internalized GPC can be hydrolyzed to release Pi. To determine if GPC import and subsequent metabolism affect phosphate homeostasis upon Pilimitation, we monitored growth and phenotypic outputs in cells provided with either Pior GPC. Inpho84∆/∆ mutant cells that exhibit phenotypes associated with Pilimitation, GPC provision rescued sensitivity to osmotic and cell wall stresses. The glycerophosphodiesterase Gde1 was required for phenotypic rescue of osmotic stress by GPC provision. GPC provision, like Piprovision, resulted in repression of the PHO regulon and activation of TORC1 signaling. Piuptake was similar to GPC uptake when phosphate availability was low (200 µM). While available at lower concentrations than Piin the human host, GPC is an advantageous Pisource for the fungus because it simultaneously serves as a choline source. In summary, we find GPC is capable of substituting for PiinC. albicansby many though not all criteria and may contribute to phosphate availability for the fungus in the human host. IMPORTANCECandida albicansis the most commonly isolated species from patients suffering from invasive fungal disease.C. albicansis most commonly a commensal organism colonizing a variety of niches in the human host. The fungus must compete for resources with the host flora to acquire essential nutrients such as phosphate. Phosphate acquisition and homeostasis have been shown to play a key role inC. albicansvirulence, with several genes involved in these processes being required for normal virulence and several being upregulated during infection. In addition to inorganic phosphate (Pi),C. albicanscan utilize the lipid-derived metabolite glycerophosphocholine (GPC) as a phosphate source. As GPC is available within the human host, we examined the role of GPC in phosphate homeostasis inC. albicans. We find that GPC can substitute for Piby many though not all criteria and is likely a relevant physiological phosphate source forC. albicans.
Mishra, Abhishek, Forche, Anja, and Anderson, Matthew Z. Parasexuality of Candida Species. Retrieved from https://par.nsf.gov/biblio/10396901. Frontiers in Cellular and Infection Microbiology 11. Web. doi:10.3389/fcimb.2021.796929.
Mishra, Abhishek, Forche, Anja, & Anderson, Matthew Z. Parasexuality of Candida Species. Frontiers in Cellular and Infection Microbiology, 11 (). Retrieved from https://par.nsf.gov/biblio/10396901. https://doi.org/10.3389/fcimb.2021.796929
@article{osti_10396901,
place = {Country unknown/Code not available},
title = {Parasexuality of Candida Species},
url = {https://par.nsf.gov/biblio/10396901},
DOI = {10.3389/fcimb.2021.796929},
abstractNote = {While most fungi have the ability to reproduce sexually, multiple independent lineages have lost meiosis and developed parasexual cycles in its place. Emergence of parasexual cycles is particularly prominent in medically relevant fungi from the CUG paraphyletic group of Candida species. Since the discovery of parasex in C. albicans roughly two decades ago, it has served as the model for Candida species. Importantly, parasex in C. albicans retains hallmarks of meiosis including genetic recombination and chromosome segregation, making it a potential driver of genetic diversity. Furthermore, key meiotic genes play similar roles in C. albicans parasex and highlights parallels between these processes. Yet, the evolutionary role of parasex in Candida adaptation and the extent of resulting genotypic and phenotypic diversity remain as key knowledge gaps in this facultative reproductive program. Here, we present our current understanding of parasex, the mechanisms governing its regulation, and its relevance to Candida biology.},
journal = {Frontiers in Cellular and Infection Microbiology},
volume = {11},
author = {Mishra, Abhishek and Forche, Anja and Anderson, Matthew Z.},
}
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